Re: 84cj w/ 350! its damn slow, what gears to use??
OK, "run over" let's say the guy has a mild 350 (200hp, 300ft/lbs) In first-low with the t-4 and the 300 with the 4.10's they are talking about putting in you get a total torque multiplication(less a 10% loss for drivetrain drag) of over 11,000 ft/lbs at the axleshafts at peak torque. That's a lot of oomph on a 1.250" axleshaft. Almost 2900 ft/lbs at the pinion stem and pushing the teeth of the ring and pinion. The 20 is a pretty good axle, but thats a lot of load. Especially if it takes a bounce and goes through a loaded-unloaded-loaded cycle.
The 12 bolt GM made it's reputation in muscle cars, not 4wd's. It never saw the loads a built 4x4 sees. It is a great axle for it's use, but that doesn't mean a 20 is bulletproof because they have the same ring gear dia. Guys who wheel GM trucks swap out their 12 bolts (which have a smaller pinion stem than the car version) for 14 bolts, 60's, and 70's.
From what little you have in your profile and in your posts it sounds like you have a pretty decent rig, and the fact that your 20 has lived so long is a testament to how tough a 20 really is. But if you wheel it as hard as you say you do (much harder than any of us "lightweights" here to hear you tell it) it is only a matter of time before that 20 is going to give it up. I'm surprised it has lived very long at all turning 40's. Better start saving up friend, your gonna need one of those "$4000 dollar" Dana 60's. If you stick around on this board, and lighten up a little, you may learn how build your own 60 for quite a bit less.
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